Configuration strict mode raise on non existing files (#375)

* Update from_yaml() * Refactor YAML environment variables interpolation * Update from_ini() * Refactor UNDEFINED * Update from_env() * Update from_dict() * Update docs * Update changelog

Author: rmk135

docs/main/changelog.rst

@@ -13,6 +13,8 @@ Development version
  default YAML loader.
 - Make security improvement: change default YAML loader to the custom ``yaml.SafeLoader`` with a support
  of environment variables interpolation.
+- Update configuration provider ``.from_*()`` methods to raise an exception in strict mode if
+ configuration file does not exist or configuration data is undefined.
 - Fix a bug with asynchronous injections: async providers do not work with async dependencies.
  See issue: `#368 <https://github.com/ets-labs/python-dependency-injector/issues/368>`_.
  Thanks `@kolypto <https://github.com/kolypto>`_ for the bug report.

docs/providers/configuration.rst

@@ -168,7 +168,42 @@ on access to any undefined option.
  :lines: 3-
  :emphasize-lines: 12
 
-You can also use ``.required()`` option modifier when making an injection.
+Methods ``.from_*()`` in strict mode raise an exception if configuration file does not exist or
+configuration data is undefined:
+
+.. code-block:: python
+ :emphasize-lines: 10,15,20,25
+
+ class Container(containers.DeclarativeContainer):
+
+ config = providers.Configuration(strict=True)
+
+
+ if __name__ == '__main__':
+ container = Container()
+
+ try:
+ container.config.from_yaml('./does-not_exist.yml') # raise exception
+ except FileNotFoundError:
+ ...
+
+ try:
+ container.config.from_ini('./does-not_exist.ini') # raise exception
+ except FileNotFoundError:
+ ...
+
+ try:
+ container.config.from_env('UNDEFINED_ENV_VAR') # raise exception
+ except ValueError:
+ ...
+
+ try:
+ container.config.from_dict({}) # raise exception
+ except ValueError:
+ ...
+
+You can also use ``.required()`` option modifier when making an injection. It does not require to switch
+configuration provider to strict mode.
 
 .. literalinclude:: ../../examples/providers/configuration/configuration_required.py
  :language: python